I think that my course work, and especially the course work I did beyond general biology, chemistry and physics helped me *far* more than the prep class I took.
The prep course was undoubtedly valuable, but it was just a refresher.
Ya...the prep course is just a refresher for what you already know (and a little bit of learning things you never paid attention to before). Without the classes themselves I think I would have done poorly.
My advice for you is to pay full attention in courses...imagine that your studying for the course doubles as studying for the MCAT
I took it without a prep course and with Gen Chem I, Cell Bio, Physics I, and Genetics...also had taken half of Gen Chem II, but withdrew at the time, so I never completed the class. I got a pretty good 32, with nothing below 10.
A bit of a non-traditional applicant.. I took the mcat with essentially no pre-reqs. I've taken the first half of intro chem, no physics, no org., and only a few biology courses. I did take the princeton review prep course, and found the materials they gave really useful.. ended up with a 29
Another non-trad here. I came from an engineering background, and knew I would need (1) to take the MCAT and (2) take all of the pre-reqs that engineering did not cover (which was limited to general chem I/II and physics I/II about ten years prior).
For timing reasons, I did not want to take the courses, take the MCAT, and then apply the next year - that is two years of waiting from the time I made the decision (about mid June) and I figured I could crunch that down to one.
So I read that big Kaplan review book in July, took the MCAT in August, and then started pre-req courses (bio I/II, biochem, organic chem, and added A&P, comparative A, genetics, micro etc. since I had the time). Managed to pull a low 30's so I was pretty satisfied.